An agricultural harvester known as a “combine” is historically termed such because it combines multiple harvesting functions with a single harvesting unit, such as picking, threshing, separating and cleaning. A combine includes a header which removes the crop from a field, and a feeder housing which transports the crop matter into a threshing rotor. The threshing rotor rotates within a perforated housing, which may be in the form of adjustable concaves, and performs a threshing operation on the crop to remove the grain. Once the grain is threshed it falls through perforations in the concaves and is transported to a grain pan. From the grain pan the grain is cleaned using a cleaning system, and is then transported to a grain tank onboard the combine. The cleaning system includes a cleaning fan which blows air through oscillating sieves to discharge chaff and other debris toward the rear of the combine. Non-grain crop material such as straw from the threshing section proceeds through a straw chopper and out the rear of the combine. When the grain tank becomes full, the combine is positioned adjacent a vehicle into which the grain is to be unloaded, such as a semi-trailer, gravity box, straight truck, or the like; and an unloading system on the combine is actuated to transfer the grain into the vehicle.
Typically, the header includes one or more knife assemblies, which can form portions of cutter bars, which cut the crop material growing in the field for collection. The knife assemblies together often define widths close to the largest width of the combine, relative to forward motion, in order to cut as much crop material as possible in each pass of the combine in the field. As combines become larger to reduce the number of passes necessary to harvest an entire field, the headers have also increased dramatically in width. While this is beneficial during crop collection in the field, increasing the width of the header has accompanying technical challenges.
One particular challenge faced by increasing header widths is increasing loads on the system driving the knife assemblies. As is known, the knife assemblies are typically driven in a reciprocating manner with a relatively high frequency, which can produce significant stress and vibration on the knife assemblies as well as the knife drive system reciprocating the knife assemblies. As headers become wider, the knife assemblies also become wider, which increases the stress and vibration that can occur on components of the knife assemblies and knife drive system due to the increased weight of the knife assemblies. One possible solution to reduce stress and vibration caused by increasing knife assembly width is lowering the weight of the knife assemblies, but this can cause knife assembly durability issues. Further, the power requirements for driving such large knife assemblies also increase, requiring a larger gearbox in the knife drive system to handle the input power and reciprocate the knife assemblies, which can limit the design options of other header components due to the limited space in the area of the header where the gearbox typically resides.
What is needed in the art is a header which can scale to a larger width while avoiding some of the issues associated with scaling up the width of known headers.